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Forum Index : Microcontroller and PC projects : help
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| brucedownunder2 Guru  Joined: 14/09/2005 Location: AustraliaPosts: 1548 |
I admire you guys .. Have you ever thought of giving us "not so gifted" controller guys a hand ? What I'm asking is how about a few of you get your caps on and help us by you developing a rpm controlled brake/slow down gismo/furling thingo. We ,for ever, have had this problem with our mill,s going into overspeed and busting blades or even worse,bringing the tower down. I'm thinking along the lines of a motorcycle hydraulic operated disc brake /caliper. You guys develope,I pay, something that could be up the top or in my control/meter room, to keep this wild bull mill from screaming it's blades off .. What do you reckon , bet it would be a walk in the park for you techo's ,lol. no issue with wiring,or it could be remote with a small battery pak and solar cell up the top for the actuator control . Thanks Bruce Bushboy |
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Grogster Admin Group  Joined: 31/12/2012 Location: New ZealandPosts: 9066 |
Yeah, if you had the likes of a photo-interrupter, or perhaps even better - a hall-effect sensor and magnet arrangement on the prop shaft to calculate the RPM's, then you could feed that into a MicroMite, which upon exceeding a certain RPM figure, could trip a brake of some kind. Concept sounds easy enough, but actually building it would require some thinking in the brake department. Using a bike brake handle, calliper, disc and hydraulics is a great idea, and should be reasonably easy to adapt to your windmill - I assume this is what you wanted it for. You'd have to have some way of working the brake-handle from the bike, but I dear-say that would not be that difficult to engineer - powerful servo or the guts of a cars' electric window mechanism perhaps? I thought that most installs of windmills have over-speed regenerative braking? Smoke makes things work. When the smoke gets out, it stops! |
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| brucedownunder2 Guru Joined: 14/09/2005 Location: AustraliaPosts: 1548 |
Thanks Grogstar. Been thinking that a anamoneter (can't spell ) wind thingo up there could measure the wind speed and regulate the on/off/slowing mech. I have all of that stuff here. Big stainless disc ,, hydraulic operated caliper and pads , brake line and resavoir and the master cylinder with a push rod actuator. I have a well equipped workshop to do any turning ,milling welding ,wiring ETC. just the "smarts' in a box or down in my work area that can be operated remotely would be the cream that I'm after . Also , I thought of a function on the "smarts" box to test the operation ,just to confirm all is ready for the strong wind event.. and turn it on,to lock it permanently if I go away for more than a few days. Your last remark --furling on most winmills-- Yes, be sadly , I and many have had some bad experiences with these "wishfull thinking" arrangements. Bruce Bushboy |
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| hitsware Guru Joined: 23/11/2012 Location: United StatesPosts: 535 |
Seems like some sort of centifugal system might be appropos..... Sans the electronics if possible. Are you talking about windmills ? |
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| brucedownunder2 Guru Joined: 14/09/2005 Location: AustraliaPosts: 1548 |
Thanks Hitsware. Yes small domestic windmill generators.Say up to around 3Kw. You might be onto something here ,Centrifugal clutch. We'd have to devise a way of working it in reverse , so that , when the mill gets to a scary rpm ,the centrifugal clutch operates and a solinoid operates to operate the brake/furling system . Bruce. 
Bushboy |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9066 |
How fast is too fast? One of those self-engaging centrifugal clutches they have on reel type lawn mowers MIGHT be useful here... They are designed to engage at any engine RPM above idle, so may well be suitable, depending on how fast you think is too fast for the prop shaft. If there is not too much in the way of mass to have to slow down(the prop and shaft are reasonably light), then perhaps we can come up with something simple and non-hydraulic. On the other hand, if there is a bit of mass in the prop-shaft, then stopping that mass may indeed require the efforts of hydraulics. Smoke makes things work. When the smoke gets out, it stops! |
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OA47 Guru Joined: 11/04/2012 Location: AustraliaPosts: 911 |
Bruce, thinking laterally, can you use an electric braking system, such as disconnecting the regulator and forcing a short circuit across the generator momentarily? It may be possible to activate this procedure once a specific output voltage is measured if the output is proportional to the revs. Just thinkin' GM |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9066 |
Yes, Graeme, that is a good idea too. 
Perhaps a MicroMite RPM meter, and once the RPM's are exceeded, it could trip a relay or contactor(big commercial relay, in essence) if the currents are large to disconnect the genny from the regulator, and short-out the genny as Graeme suggests. ALL IN THEORY THOUGH! - Some motors or genny's would NOT thank you for shorting them at speed - with the currents potentially flowing at high RPM's, suddenly shorting them out might cause fatal injuries to the motor windings.  Smoke makes things work. When the smoke gets out, it stops! |
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| brucedownunder2 Guru Joined: 14/09/2005 Location: AustraliaPosts: 1548 |
Thanks Graeme and Grogstar,(what a wonderful name) . Shorting out the windings is probably a no-no? . as our original poster on the windmill stion told us he has ,I think , burn't his windings out to a short and therefore the magnetic flux in the windings prevents the rotor from turning ,,nt a good look. The centrifugal clutch method (in reverse,if someone can explain how to arrange this), looks a go . I do realise this is a "Windmill" topic and would like to continue ,but maybe Glenn could show me or double up on all the postings ,so the windmill guys are in the picture.. I mean insert them into the windmill section as well?. Thanks all for your interest Bruce Bushboy |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9066 |
With the centrifugal clutch idea - Bolt one side of the clutch to the mount - it cannot turn. Clamp your prop-shaft to the other free-spinning end of the clutch. If the RPM's of the prop-shaft try to rise too high, the centrifugal clutch will start to operate, and will auto-brake the prop-shaft speed. This does depend on if the minimum RPM of the clutch unit, is within the speed limit you need for the prop-shaft. Smoke makes things work. When the smoke gets out, it stops! |
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Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5019 |
The problem with using brakes on a wind turbine is they need to be able to brake much much more than you expect. This is because the power in the wind is the cube of air speed. So in simple terms, a doubling of wind speed means 8 times the power you need to deal with. So if you have a windmill thats rated for 1kw at 30kmh, but the wind speed has increased to 60kmh, then you need to contain 8kw of power. So shorting a alternator thats designed for 1kw, will quickly expire in smoke when its asked to absorb 8kw. If the wind increases to 90khm, then you have about 27kw. Thats why electrical, or even mechanical, braking of the turbine in high winds is doomed to fail. And its also why any turbines with a electrical brake ( shorting switch ), the brake should only be used if the winds are light. The idea is you short out the alternator before the strong winds arrive. It works because a slow moving turbine is in a stalled state, the blades are making very little power, and cant push the shorted alternator up to speed ( usually ). Unfortunately once a turbine is up to speed in winds greater than the alternator is rated for, your only options are to furl the tail, which will turn the turbine out of the wind, or feather the blades, so the turbine looses power. For the small domestic turbine, a automatic and/or manual tail furling system is the only real option. For the bigger turbines, the blades are feathered. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| hitsware Guru Joined: 23/11/2012 Location: United StatesPosts: 535 |
> Bolt one side of the clutch to the mount - it cannot turn. > Clamp your prop-shaft to the other free-spinning end of the clutch. Ya Mon 
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palcal Guru Joined: 12/10/2011 Location: AustraliaPosts: 1804 |
From Dec 2004 to Mar 2005 Silicon Chip had a project to build a wind generator. It had some sort of self furling tail that turned the propeller out of the wind when it became too strong. The project was by Glen Littleford and was described on The Back Shed. Paul. Edit. For those wondering how it worked, I briefly read the article. The propeller is offset on the mast by about 100mm, when the wind hits the propeller it has a tendency to twist around out of the wind. The tailplane is hinged probably held by a spring. It holds the propeller into the wind until the wind is strong enough to overcome the force of the tail. (I think). The windmill came as a kit there were some drawings but from what I could see the details of the tail were sketchy. Paul "It is better to be ignorant and ask a stupid question than to be plain Stupid and not ask at all" |
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| brucedownunder2 Guru Joined: 14/09/2005 Location: AustraliaPosts: 1548 |
OK, better get off this subject --it's not really anything to do with micro-controllers,Etc. Anyhow, lastly, here's a pic of what I thought I might do some years back.. Still have plenty of this stuff ,,,so may fiddle a bit more. Thanks for you guys ,but i really don't think you are into what i wanted. End. Bruce Bushboy |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9066 |
That is not to say we are not interested - I am!
Going on what Glenn has posted in the previous page, perhaps your bike brake idea really is the best - those brakes are designed to be able to stop a lot of moving mass and energy, so.... Where there is a will, there is a way! Smoke makes things work. When the smoke gets out, it stops! |
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| brucedownunder2 Guru Joined: 14/09/2005 Location: AustraliaPosts: 1548 |
Thanks grogstar,, I didn't mean to be rude, I sort just came to the conclusion that maybe I was "off-topic" a bit ,within this section . My original idea was some sort of sophiscated micro-controller that senses the wnd strength/power and convert this data into a brake controller ---like a car going down a steep mountain range -brake is not on all the time ,just keeping the car under control . And maybe after a period the controller decides to brake completly for an hour or more ,until that wind event passes. If you are at home ,no problems,you do it.. but it's when it's(windmill) is unattended ,,thats when this "controller could be a real help. Thanks for your interest, thats a motorcycle disc brake and caliper in the Pic. Bruce Bushboy |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9066 |
Yes, I for one, am interested in this idea, cos I also am a backshed mechanic, and love tinkering with my cars at the weekends, when I am not doing electronic kinds of things!
I would be interested to hear Glenn's thoughts on the bike brake concept, cos this would be able to exert a lot of stopping force, so one would THINK that this would be sufficient to slow or stop an prop which was approaching over-speed... Even considering the figures he mentioned. False logic perhaps? Smoke makes things work. When the smoke gets out, it stops! |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5019 |
I think provided the brake is big enough to pull up the turbine, and we are talking several horsepower, and locks it down so its not slipping and cooking the brake pads, then it could work. Ideally, the "control" would measure wind speed, and once a certain level is reached for a preset time, would go into brake mode until the wind speeds have subsided, for another preset time. You want to avoid false triggering, like if a little willy willy went past the tower, and you want to make sure the storm winds have passed before letting the turbine spin up again. Also need to consider how to activate the brake mechanism. Going to need a few kg of force, so a geared motor? Would be a fun project. The automatic tail furling system used on small wind mills is the simplest, with only one moving part, but bit of a black art to get it working right. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9066 |
That's also a good point. You can get some pretty powerful geared motors on eBay for not much cash - I am using one in my model elevator project as the hoist motor. I guess you'd need a proportionally bigger one for the extra force needed to pull the brake handle in, but the wee one I am using is a 12v 45RPM one, and it can hoist a couple of KG's no problem under test. Slower RPM geared motor would be better - more torque. In my case, the 45RPM one was perfect, as with PWM control, the motor can be made to have very smooth ramp-up and ramp-down, and if it is too fast at full power, the PWM can be used to set a slower maximum too. You could use a photo-interuptor to sense the maximum travel of the brake handle, or perhaps even just a micro-switch as a limit-switch.(to prevent the motor from trying to pull the handle in too far) Smoke makes things work. When the smoke gets out, it stops! |
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| shoebuckle Senior Member  Joined: 21/01/2012 Location: AustraliaPosts: 189 |
A physical brake is one way, which will convert the excess energy into heat (which will be lost). How about attaching a generator/alternator and increasing the load to slow the mill down. The electricity generated could be captured in a battery (or fed back into the grid) and reused. This is what hybrid cars do very effectively. Cheers, Hugh |
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